THE VARIATION OF FLY ASH COMPOSITION SINCE THE BEGINNING OF LIGNITE EXPLOITATION IN AMYNTEON, GREECE AND THE CASE OF COFIRING WITH XYLITE

摘要

In the current study, the evolution of the composition of fly ash, since the beginning of the operation of the lignite-fired power station of Amynteon-Filotas [Steam Electric Station (SES) Amynteon-Filotas] in Greece, is presented. This power station began to operate in 1987. Prior its operation, it had been judged -according to the quality characteristics of feedcoal-that fly ash would turn from calcareous to barely pozzolanic. Apart from that, the alteration of the percentages of sulphur (both total and volatile) in feedcoal had revealed that fly ash would not usually meat the specifications to be used in the production process of concrete, due to the excessive percentage presence of SO3. These predictions were eventually confirmed during the 23 years of operation of the power station. Over these years, the percentage presence of SO3 kept alternating, rendering -in some cases-ash suitable for use in cement industry applications. The periodical changes in the concentration of SO3 in fly ash are attributed to the free (volatile) sulfur of feedcoal as well as to the excess of FeS2, which has also a serious effect on the daily power production process (severe erosion of the metallic surfaces of boiler). Some possible solutions for tackling this phenomenon are also suggested through this study: discard of specific FA grain fractions, intense monitoring of the material and its effective mixture-homogenization and selective mining of lignite.